Doctor of Philosophy (PhD)
Burkholderia glumae is a Gram-negative bacterium causing bacterial panicle blight (BPB) in rice. BPB can cause severe damage to rice and reduce rice yield up to 75%, while no effective treatment has been developed to control the disease. B. glumae produces and secretes an essential virulence factor, toxoflavin, which is mainly responsible for the symptoms of BPB. Synthesis and transport of toxoflavin are regulated in a quorum-sensing dependent manner. Members of the DedA superfamily are putative membrane transporters and found in nearly all species. Mutation of dedA in Burkholderia species results in sensitivity to colistin, an antibiotic belonging to the cationic antimicrobial peptide (CAMP) family. The dedA of Burkholderia species has been renamed dbcA (dedA required for Burkholderia CAMP resistance). The aim of this dissertation is to investigate the function of DbcA in quorum sensing and virulence of B. glumae. The deletion of dbcA caused pleiotropic effects in B. glumae including colistin sensitivity, reduced toxoflavin production, and loss of virulence. The deletion of dbcA from B. glumae genetically altered the proton motive force (PMF), which subsequently caused B. glumae ΔdbcA to become less virulent in several BPB infection models. Sodium bicarbonate also chemically altered the PMF and reduced virulence of B. glumae. Oxalic acid is a “common good” required for growth, quorum-sensing, and virulence of B. glumae. B. glumae produces and secretes oxalic acid to neutralize the ammonia-mediated alkaline pH toxicity in culture media. B. glumae ΔdbcA secreted less oxalic acid and was unable to acidify culture media at stationary phase. B. glumae ΔdbcA accumulated less quorum sensing molecules at alkaline pH. Toxoflavin biosynthesis and transport operons were downregulated in B. glumae ΔdbcA. In addition, B. glumae ΔdbcA was also sensitive to several divalent cations which are important components of plant innate immunity. Alteration of PMF with sodium bicarbonate also reduced oxalic secretion and quorum sensing in B. glumae. Overall, the data showed that DbcA is required for maintaining proper PMF, which is critical for quorum sensing and virulence of B. glumae. Moreover, this study also indicated that sodium bicarbonate can be an important chemical for treatment of BPB in rice.
Iqbal, Asif, "A Membrane Transporter Required for Quorum Sensing and Virulence of the Rice Pathogen Burkholderia Glumae" (2022). LSU Doctoral Dissertations. 5985.
Doerrler, William T.
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